We’re recorded a demo (MIDI & audio) in A5 without regard to the session’s tempo, because we didn’t know it (so, it’s at the default 120 BPM). Now that we know the tempo (from tap tempo over the playback), I need to adjust the session’s tempo to 90 BPM without affecting the MIDI. In the same way that changing the tempo doesn’t affect audio.
Hope that makes sense. Let me know if you need clarification.
As a side question, is it possible to type in a numeric value somewhere for the time stretch? Let’s say I want twice the length (if I go e.g. from 90 BPM to 180 BPM), can I just click somewhere and write 200%? In the region name after the stretch there is a reference to the time-stretch, after all (region-name @200).
I’m not sure, I actually just started with Ardour but I think there’s a transform function for that (Edit > MIDI > transform). I’ll have to check the manual. Maybe it can also be used for OP’s question ?